Phospholipids and glycolipids

Fats (triacylglycerol, 1) are esters of glycerol with three fatty acids (see p.48). Within the cell, they mainly occur as fat droplets. In the blood, they are transported in the hydrophobic interior of lipoproteins (see p. 278). 

Phospholipids (2) are the main constituents of biological membranes (see pp. 214-217). Their common feature is a phosphate residue that is esterified with the hydroxyl group at C-3 of glycerol. Due to this residue, phospholipids have at least one negative charge at a neutral pH. 

Phosphatidates (anions of the phosphatidic acids), the simplest phospholipids, are phosphate esters of diacylglycerol. They are important intermediates in the biosynthesis of fats and phospholipids (see p. 170). Phosphatidates can also be released from phospholipids by phospholipases. 

The other phospholipids can be derived from phosphatidates (residue = phosphatidyl). Their phosphate residues are esterified with the hydroxyl group of an amino alcohol choline, ethanolamine, or serine) or with the cyclohexane derivative myo-inositol. Phosphatidylcholine is shown here as an example of this type of compound. When two phosphatidyl residues are linked with one glycerol, the result is cardiolipin (not shown), a phospholipid that is characteristic of the inner mitochondrial membrane. Lysophospholipids arise from phospholipids by enzymatic cleavage of an acyl residue. The hemolytic effect of bee and snake venoms is due in part to this reaction. 

Phosphatidylcholine (lecithin) is the most abundant phospholipid in membranes. Phosphatidylethanolamine (cephalin) has an ethanolamine residue instead of choline, and phosphatidylserine has a serine residue. In phosphatidylinositol, phosphatidate is esterified with the sugarlike cyclic polyalcohol myo-inositol. A doubly phosphorylated derivative of this phospholipid, phosphatidylinositol 4,5-bisphosphate, is a special component of membranes, which, by enzymatic cleavage, can give rise to two second messengers, diacylglycerol (DAG) and inositol l,4,5trisphosphate (InsPsi see p.386). 

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Malachite green (0.0...2.0) uracil derivatives, triazine herbicides [163] polar lipids [246, 247] phospholipids [248, 249] fatty acids, fatty aldehydes, phospholipids and glycolipids [250] microbiocidal isothiazolones [251]... 

Whole-Cell FTMS Glyceride, Phospholipid, and Glycolipid Elucidation... 

One major pathway leads from acetyl-CoA to the activated fatty acids (acyl-CoA for details, see p.l68). Fats, phospholipids, and glycolipids are synthesized from these, and fatty acid derivatives in particular are formed. Quantitatively, this is the most important pathway in animals and most plants. 

Complex lipids, such as neutral fats (triacyl-glycerols), phospholipids, and glycolipids, are synthesized via common reaction pathways. Most of the enzymes involved are associated with the membranes of the smooth endoplasmic reticulum. 

A second esterification of this type leads to a phosphatidate (enzyme l-acylglycerol-3-phosphate acyltransferase 2.3.1.51). Unsaturated acyl residues, particularly oleic acid, are usually incorporated at C-2 of the glycerol. Phosphatidates (anions of phosphatidic acids) are the key molecules in the biosynthesis of fats, phospholipids, and glycolipids. 

Membranes of plant and animal cells are typically composed of 40-50 % lipids and 50-60% proteins. There are wide variations in the types of lipids and proteins as well as in their ratios. Arrangements of lipids and proteins in membranes are best considered in terms of the fluid-mosaic model, proposed by Singer and Nicolson % According to this model, the matrix of the membrane (a lipid bilayer composed of phospholipids and glycolipids) incorporates proteins, either on the surface or in the interior, and acts as permeability barrier (Fig. 2). Furthermore, other cellular functions such as recognition, fusion, endocytosis, intercellular interaction, transport, and osmosis are all membrane mediated processes. 

During the extraction process three types of interactions are usually disrupted, these are van der Waals forces in lipid-lipid, lipid-protein, and liquid-carbohydrate complexes electrostatic and hydrogen bonding interactions between lipids andproteins andcovalent bonding between lipids, carbohydrates, and proteins (Roby t and White, 1987). The solvent of choice depends on the type of lipid and the interactions to be disrupted. Thus, neutral lipids may be extracted with nonpolar solvents, while phospholipids and glycolipids are extracted with more polar solvent mixtures (Shahidi and Wanasundara, 1998). 

Since the synthesis of glycolipids involves the synthesis of both the lipid and the oligosaccharide portions, we shall also discuss that part of the recorded lipid synthetic work which has involved the use of carbohydrates. In fact, some of the first-recorded applications of carbohydrate molecules as chiral templates are to be found in the lipid field particularly with the use of 1,2 5,6-di-O-isopropylidene-D-mannitol [33] as a precursor of chiral glycerol derivatives for the synthesis of phospholipids and glycolipids based on glycerol and with the use of glucosamine derivatives for the synthesis of phytosphingosines [34] and since this area has not previously been reviewed, it will be treated with a more historical perspective. 

Gigg R (1983) Phospholipids and Glycolipids, in Ansell MF (ed) Supplement to 2nd ed of Rodd s Chemistry of Carbon Compounds vol IE, Elsevier, Amsterdam, p 425... 

Fatty acids are long carbon chains with a carboxylic acid end. They serve three basic functions in the human body 1. they serve as hormones and intracellular messengers (he. eicosanoids such as prostaglandins) 2. they are components of the phospholipids and glycolipids of cell membranes 3. they act as fuel for the body. The first of these functions will not be tested on the MCAT unless it is explained in a passage. For the second function of fatty acids you should be able to recognize the stnicture of a phospholipid as shown in Lecture 3 of the biology manual. 

Lipids include fatty acids (aliphatic carboxylic acids), fatty acid esters, phospholipids, and glycolipids. Plants containing lipids with anticancer properties include the following ... 

Select five from fatty acids, acylglycerols, steroids, terpenes, phospholipids and glycolipids. (a) See Table 1.5. (b) See Table 1.7. 

Figure 9.6 Chemical structure of complex lipids (e.g., phospholipids and glycolipids) which differ in that they contain additional elements (e.g., P, S, and N) or small hydrophilic compounds (e.g., sugars and certain amino acids).

Analytical methods for tocol analysis have continued to improve, as noted by Abidi (2000), and in the intervening ten years, as noted in this chapter. We predict that advances will continue to be made in the field of the chromatographic analysis of tocols. Also, we believe that lipidomic methods (quantitative analysis via direct injection tandem electrospray ionization mass spectrometry) will be developed for the rapid analysis of tocols, just as these methods have already been used for the profiling of phospholipids and glycolipids (Han, 2011 Welti, 2011). These methods usually involve the direct injection of lipid samples into a... 

Seddon JM, Robins J, Gulik-Krzywicki T, Delacroix H.ninverse micellar phases of phospholipids and glycolipids. Phys. Chem. Chem. Phys. 2000 2 4485-4493. 

Phospholipids and Glycolipids Readily Form Bimolecular Sheets in Aqueous Media... 

The favored structure for most phospholipids and glycolipids in aqueous media is a bimolecular sheet rather than a micelle. The reason is that the two fatty acyl chains of a phospholipid or a glycolipid are too bulky to fit into the interior of a micelle. In contrast, salts of fatty acids (such as sodium palmitate, a constituent of soap), which contain only one chain, readily form micelles. The formation of bilayers instead of micelles by phospholipids is of critical biological importance. A micelle is a limited structure, usually less than 20 nm (200 A) in diameter. In contrast, a bimolecular sheet can have macroscopic dimensions, such as a millimeter (10 nm, or 10 A). Phospholipids and related molecules are important membrane constituents because they readily form extensive bimolecular sheets (Figure 1211). 

Fatty acids are physiologically important as (1) components of phospholipids and glycolipids, (2) hydrophilic modifiers of proteins, (3) fuel molecules, and (4) hormones and intracellular messengers. They are stored in adipose tissue as triacylglycerols (neutral fat). 

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